Diabetics are particularly prone to presenting serious ischemic processes that usually affect the more distal vessels (infrapopliteal location), i.e., those vessels belonging to the patient's lower limbs. It is referred to as critical lower limb ischemia. The distal location of lesions in the lower limbs makes the surgical or endovascular revascularization thereof difficult, so in a large proportion of these patients, due to the anatomical extension and distribution of arterial occlusive disease, the ischemia continues its inexorable course until causing amputation of the affected limb.
Standard treatment today for these patients in whom surgical or endovascular revascularization are impossible includes pharmacological treatments. However, it has not yet been proven that pharmacological treatments improve the symptoms of lower limb ischemia. Alternatively, cell therapy and gene therapy have been developed in recent years. The advantage of cellular administration in angiogenesis induction is that it could promote vascular and tissue regeneration directly, as well as the release of different angiogenic growth factors.
In this context, for the purpose of monitoring the patient's progression and making the most suitable medical decisions, it is very important to obtain information relating to whether or not angiogenesis is taking place after administration of the treatment. Angiogenesis can briefly be defined as the physiological process consisting of the formation of new blood vessels from preexisting vessels. In order to determine if angiogenesis is in fact taking place, the “gold standard” technique considered today is arteriography.
Essentially, an arteriography starts by puncturing and catheterizing an artery (usually the common femoral artery) using to that end the Seldinger technique (see “Catheter replacement of the needle in percutaneous arteriography. A new technique.” Acta Radiol. (Stockholm), 39, 368, 1953). Subsequently, a multiperforated catheter is placed in the infrarenal abdominal aorta on the level of vertebral body L3 and successive X-ray series are taken with iodinated contrast focused on both lower limbs. The contrast material is entrained by the blood flow of the artery and gradually opacifies the network of arteries from a larger to a smaller size until reaching the tissues. Finally, the venous return of the contrast material takes place.
Throughout this entire process, successive flat images of the limbs in question are acquired by means of a digital angiograph. The acquired images have a aspect similar to that shown in FIGS. 1a-1e, where it can be seen how the contrast starts to reach the arteries of the patient's lower limbs (FIGS. 1a and 1b) until reaching a maximum (FIG. 1c), after which the contrast starts to be withdrawn by the venous route (FIGS. 1d and 1 e). These figures allow seeing where the blood flow reaches at a point in time before starting treatment and they allow comparison with equivalent images from the same patient taken after administering treatment. For example, images can be taken before starting treatment and then be repeated 6 or 12 months later. However, this method has various drawbacks, some of which are mentioned below.
Firstly, it is an invasive procedure, meaning that it involves arterial puncturing and catheterization with its subsequent risks. As a result, it furthermore requires hospitalization for at least 24 hours in order to monitor and control the puncture area.
Secondly, it is not easy to get the images obtained before the treatment and the images obtained in subsequent controls to match up entirely, primarily due to the patient's movements at the time of acquiring the images, among other causes. As a result, the position and trajectory of the patient's different arteries do not exactly match up in both images, which often times makes a correct comparison difficult. Today there is software called “Metamorph” (“Angiographic Demonstration of Neoangiogenesis Alter Intra-arterial Infusion of Autologous Bone Marrow Mononuclear Cells in Diabetic Patients UIT Critical Limb lschemia,” Cell Transplantation, Vol. 20, p. 1629-1639, 2011) created specifically for this purpose. However, this software requires the two images to be compared to be identical, and after thorough testing, it has had to be ruled out because this is not possible in most cases.
Thirdly, even though the images obtained using arteriography allow observing the arteries having at least a given minimum size with relative clarity, it is impossible to view the smaller vessels, such as capillaries for example. This is an important drawback for the evaluation of the angiogenesis, because the improvement sometimes occurs precisely as a result of the generation of capillaries, without there being observable changes in larger vessels.
Finally, the comparative study between images taken before and after treatment is performed today in a completely “subjective” manner by visually assessing the presence or absence of new vessels or growth of preexisting vessels (angiogenesis). Furthermore, arteriography does not provide quantifiable data with respect to tissue perfusion.